Talking photons on quantum quest
The delicate dance of two photons has allowed researchers to clear one more hurdle on the long path to the quantum-computing future.
For the first time, one photon of light has been made to directly alter another.
This is an important step, as getting light to influence light will likely play a big role in any photon-based computing system.
Normally, light passes directly through other beams of light and it hardly interacts at all with itself. This is useful for application such as sending information down optical cables, where it is disinclined to lose anything or become garbled on the way.
It is not a useful property if you want to make a photonic logical gate, for instance.
But Vienna University of Technology (TU Wien) researchers have proved the possibility of such a device, by bringing together a pair of photons in the strongest coupling possible, during a recent experiment.
Their reports say the interaction was strong enough to change the phase of each photon by 180 degrees.
In simple terms, this was achieved by having both the photons ‘talk’ to each other via a single atom.
Photons interact reasonably well with matter, so the team created an experiment where both photons woul talk to a single Rubidium atom.
The team used carefully-engineered structures around the rig to make sure the light interacted with the atom as much as possible.
Normally, when a photon is shot at a rubidium atom, it reacts in such a way that the photon can be absorbed, saturate the system, and then be released back into the resonator.
Researchers have now shown that when a pair of photons arrives in the resonator simultaneously, one is absorbed, while the other is inverted.
“That way, a maximally entangled photon state can be created,” Arno Rauschenbeutel of the Institute for Atomic and Subatomic Physics at TU Wien said.
“It is like a pendulum, which should actually swing to the left, but due to coupling with a second pendulum, it swings to the right. There cannot be a more extreme change in the pendulum's oscillation. We achieve the strongest possible interaction with the smallest possible intensity of light.
“Such states are required in all fields of quantum optics - in quantum teleportation, or for light-transistors which could potentially be used for quantum computing,” he said.
The interaction is detailed in the journal Nature Photonics.